Why don't you just use an image for the submit button instead? That would look cooler anyway.
If you wanted to hide the text still, you could try an image replacement technique I use, though I've never tried it on an input button, so this may not work:
Name your submit button id="submit" to apply it. If that doesn't work, try:
Again, though, if you're hiding the text, it'll look like an ugly blank button (unless you're on a Mac like me and then it'd be a blank beautiful aqua button
) -- an image would probably be better:
<input type="image" src="submit.png" id="submit" name="submit" value="submit" />